Infections are a significant problem in many fields where sanitary conditions are important, such as in healthcare. Problematic infections may arise from bacterial, fungal, amoebic, protozoan and/or viral organisms. Challenges are encountered both in preventing infection, and in reducing or eliminating the infection once it is established. Infected environments may include surfaces of objects, fluids and fluid conduits and/or humans or animals.
Alcohol solutions and isopropyl alcohol wipes are commonly used to sanitize surfaces and have been shown to have antibacterial activity. The most effective inhibitory anti-microbial effect is seen with 70% isopropanol solutions. Alcohol solutions at this concentration are quite expensive and rapidly evaporate, which substantially diminishes their efficacy and increases their cost. Moreover, although isopropanol solutions may be used for surfaces, including human skin, and in a variety of medical applications, alcohol solutions of this concentration cannot be administered to humans, for medical purposes, other than topically.
In the healthcare field, infections of various types and causes are common and often result in longer hospital stays, producing higher hospital costs. Even worse, over 90,000 patient deaths annually are attributed to nosocomial infections—that is, infections acquired at a hospital or in another healthcare environment. Surveillance for nosocomial infection has become an integral part of hospital practice. Studies conducted more than 20 years ago by the Centers for Disease Control and Prevention (CDC) documented the efficacy of these surveillance activities in reducing nosocomial infection occurrence. Despite the attention paid to problems of nosocomial infection, however, infection rates have not been dramatically reduced, and nosocomial infections remain a substantial risk and a substantial health concern.
One problematic source of infections in the medical and veterinary fields is found in catheters, and particularly in in-dwelling catheters. Catheters have become essential in the management of critical care patients, yet the inside of a catheter is often the major source of infection. Catheters are used for delivery of fluids, blood products, drugs, nutrients, hemodialysis, hemofiltration, peritoneal dialysis, retrieval of blood samples, monitoring of patient conditions, etc. Transcutaneous catheters often become infected through skin penetration of the catheter. It has been found that seventy percent (70%) of all nosocomial bloodstream infections occur in patients with central venous catheters. Daouicher et al. 340, 1-8, NEW ENGLAND JOURNAL OF MEDICINE (1999).
In particular, during some procedures, a catheter must be implanted in, and remain implanted in, a patient for a relatively long period of time, e.g. over thirty days. Intravenous (IV) therapy catheters and urinary catheters typically remain implanted for a substantial period of time. As a result of trauma to the areas of insertion, and pain to the patients, such catheters can't be removed and implanted frequently. Catheter-borne bacteria are implicated as a primary source of urinary tract infections. Patients who receive a peripherally inserted central catheter during pregnancy have also been found to be at significant risk for infectious complications. “Complications Associated With Peripherally Inserted Central Catheter Use During Pregnancy” AM. J. OBSTET. GYNECOL. 188(5):1223-5 May 2003. In addition, central venous catheter infection, resulting in catheter related sepsis, has been cited as the most frequent complication during home parenteral nutrition. CLINICAL NUTRITION, 21(1):33-38, 2002. Because of the risk of infections, catheterization may be limited to incidences when the procedure is absolutely necessary. This seriously compromises patient health.
After most prescribed access medical procedures involving a catheter, the catheter is flushed with saline and then filled with a liquid, such as saline or a heparin solution, to prevent blood from clotting inside of the catheter, to inhibit the patient's blood from backing up into the catheter, and to prevent gases from entering the catheter. The liquid that is used to flush the catheter is referred to as a “lock-flush,” and the liquid used to fill the catheter following flushing or during periods of non-use is referred to as a “lock” solution.
Traditionally, catheters have been locked with normal saline or heparin solutions, which provide anticoagulant activity. Heparin and saline are sometimes used in combination. Normal saline is generally used to lock short term peripheral intravenous catheters, but saline has no anticoagulant or antimicrobial activity. Heparin solutions are generally used to lock vascular catheters. Heparin has anticoagulant activity but it does not function as an antimicrobial and does not prevent or ameliorate infections. There are also strong indications that heparin in lock solutions may contribute to heparin-induced thrombocytopenia, a serious bleeding complication that occurs in a subset of patients receiving heparin injections.
Catheter locking solutions comprising Taurolidine, citric acid and sodium citrate have been proposed. A recent publication (Kidney International, September 2002) describes the use of a 70% alcohol solution as a lock solution for a subcutaneous catheter port. The use of alcohol as a lock solution is questionable, since it is not an anticoagulant, and since there would be risks associated with this solution entering the bloodstream. There is also no evidence that the inventors are aware of that indicates that a 70% alcohol solution has any biofilm eradication activity.
An emerging trend and recommendation from the Center for Infectious Disease (CID) is to treat existing catheter infections systemically with either a specific or a broad range antibiotic. Use of an antibiotic in a lock solution to prevent infection is not recommended. The use of antibiotics to treat existing catheter infections has certain risks, including: (1) the risk of antibiotic-resistant strains developing; (2) the inability of the antibiotic to kill sessile, or deep-layer biofilm bacteria, which may require the use of antibiotics at toxic concentrations; and (3) the high cost of prolonged antibiotic therapy. Catheters coated with an antiseptic or antibiotic material are available. These coated catheters may only provide limited protection for a relatively short period of time.
In general, free-floating organisms may be vulnerable to antibiotics. However, bacteria and fungi may become impervious to antibiotics by attaching to surfaces and producing a slimy protective substance, often referred to as extra-cellular polymeric substance (EPS). As the microbes proliferate, more than 50 genetic up or down regulations may occur, resulting in the formation of a more antibiotic resistant microbial biofilm. One article attributes two-thirds of the bacterial infections that physicians encounter to biofilms. SCIENCE NEWS, 1-5 Jul. 14, 2001.
Biofilm formation is a genetically controlled process in the life cycle of bacteria that produces numerous changes in the cellular physiology of the organism, often including increased antibiotic resistance (of up to 100 to 1000 times), as compared to growth under planktonic (free floating) conditions. As the organisms grow, problems with overcrowding and diminishing nutrition trigger shedding of the organisms to seek new locations and resources. The newly shed organisms quickly revert back to their original free-floating phase and are once again vulnerable to antibiotics. However, the free-floating organism may enter the bloodstream of the patient, creating bloodstream infections, which produce clinical signs, e.g. fever, and more serious infection-related symptoms. Sessile rafts of biofilm may slough off and may attach to tissue surfaces, such heart valves, causing proliferation of biofilm and serious problems, such as endocarditis.
In industrial settings, the formation of biofilms is very common and is generally referred to as biofouling. For example, biofilm growth on mechanical structures, such as filtration devices, is a primary cause of biological contamination of drinking water distribution systems. Biofilm formation in industrial settings may lead to material degradation, product contamination, mechanical blockage and impedance of heat transfer in processing systems. Biofilm formation and the resultant contamination is also a common problem in food preparation and processing facilities.
To further complicate matters, conventional sensitivity tests measure only the antibiotic sensitivity of the free-floating organisms, rather than organisms in a biofilm state. As a result, a dose of antibiotics is administered to the patient, such as through a catheter, in amounts that rarely have the desired effect on the biofilm phase organisms that may reside in the catheter. The biofilm organisms may continue to shed more planktonic organisms or may go dormant and proliferate later as an apparent recurrent infection.
In order to eradicate biofilm organisms through use of antibiotics, a laboratory must determine the concentration of antibiotic required to kill the specific genetic biofilm phase of the organism. Highly specialized equipment is required to provide the minimum biofilm eradication concentration. Moreover, the current diagnostic protocols are time consuming, and results are often not available for many days, e.g. five (5) days. This time period clearly doesn't allow for prompt treatment of infections. The delay and the well-justified fear of infection may result in the overuse of broad-spectrum antibiotics and continued unnecessary catheter removal and replacement procedures. Overuse of broad-spectrum antibiotics can result in the development of antibiotic resistant bacterial strains, which cannot be effectively treated. Unnecessary catheter removal and replacement is painful, costly and may result in trauma and damage to the tissue at the catheter insertion site.
The antibiotic resistance of biofilms, coupled with complications of antibiotic use, such as the risk of antibiotic resistant strains developing, has made antibiotic treatment an unattractive option. As a result, antibiotic use is limited to symptomatic infections and prophylactic antibiotics are not typically applied to prevent contamination. Because the biofilm can act as a selective phenotypic resistance barrier to most antibiotics, the catheter must often be removed in order to eradicate a catheter related infection. Removal and replacement of the catheter is time consuming, stressful to the patient, and complicates the medical procedure. Therefore, there are attempts to provide convenient and effective methods for killing organisms, and especially those dwelling inside of catheters, without the necessity of removing the catheter from the body.
In addition to bacterial and fungal infections, amoebic infections can be very serious and painful, as well as potentially life threatening. Several species of Acanthameoba, for example, have been found to infect humans. Acanthamoeba are found worldwide in soil and dust, and in fresh water sources as well as in brackish water and sea water. They are frequently found in heating, venting and air conditioner units, humidifiers, dialysis units, and in contact lens paraphernalia. Acanthamoeba infections, in addition to microbial and fungal infections, may also be common in connection with other medical and dental devices, including toothbrushes, dentures and other dental appliances, and the like. Acanthamoeba infections often result from improper storage, handling and disinfection of contact lenses and other medical devices that come into contact with the human body, where they may enter the skin through a cut, wound, the nostrils, the eye, and the like.
There are numerous different kinds of microbes that present problematic infections, including varieties of bacteria and fungi. However, present methods of eliminating infections are generally limited in the scope of the different microbes that a solution is effective against. “Inhibitory Effect of Disodium EDTA upon the Growth of Staphylococcus epidermidis In Vitro: Relation to Infection Prophylaxis of Hickman Catheters”, Root, et al., ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, November 1988, p. 1627-1633, describes the in-vitro use of disodium EDTA against a particular catheter-associated Staphylococcus epidermidis pathogen isolate.
EDTA has traditionally been useful as a metal chelator and has been used, in combination with other active compounds, for a variety of purposes. EDTA is often used, in low concentrations, as an in-vitro anticoagulant for blood specimen collection and testing and as an antioxidant synergist, and is added to solutions, for example, as a chelator, a stabilizer, or a preservative for pharmaceutical preparations. EDTA may exist in a variety of forms, some of which are sodium salt forms, such as disodium, trisodium, and tetrasodium salts and others metal chelates such as iron, copper, magnesium, etc. Certain forms of EDTA have been utilized, in conjunction with other substances as an adjuvant, in compositions for treating infected catheters. When used in a clinical setting, or in a composition that interacts with humans or animals, the solutions are generally adjusted to a generally physiological, or neutral, pH range.
A combination of an alcohol with an additive, such as a non-sodium salt form of EDTA, is described in PCT Application WO 02/05188. PCT Application, WO 00/72906 A1 describes a lyophilized mixture of an antimicrobial agent, e.g. antibiotic, and a second agent that may be non-sodium salt form of EDTA as a chelating agent for catheter flushing. In U.S. Pat. No. 5,688,516, a composition having an anticoagulant, a chelating agent, such as to EDTA and an antimicrobial agent, such as Minocycline, are described for coating medical devices and inhibiting catheter infection. In particular described examples, a disodium form of EDTA is brought to a physiological pH of 7.4 and is used in the composition. PCT Application, WO 99/09997 describes treatment of fungal infection with a combination of an antifungal agent, and a chelator, such as EDTA.
Other areas in which infections present a problem include medical devices and materials used in connection with the eyes, such as contact lenses, scleral buckles, suture materials, intraocular lenses, and the like. In particular, there has been emphasis on discovery of methods to disinfect of ocular prosthesis, e.g. contact lenses. Bacterial biofilms may participate in ocular infections and allowing bacteria to persist on abiotic surfaces that come in contact with, or are implanted in the eye. Biofilms also may form on the biotic surfaces of the eye. “The Role of Bacterial Biofilms in Ocular Infections, DNA CELL BIOL., 21(5-6):415-20, May-June 2002. A severe form of keratitis can also be initiated by a protozoan amoeba which can contaminate lens disinfectant fluids. An ophthalmic formulation of tetrasodium EDTA and alkali salts, buffered to a pH of 6-8 to disinfect contact lenses is described in U.S. Pat. No. 5,300,296. U.S. Pat. No. 5,998,488 describes an opthalmic composition of EDTA and other substances, such as cyclodextrin and boric acid.
In the dental field, items to be placed in a mouth, such as dental tools, dental and orthodontic devices such as retainers, bridges, dentures, and the like need to be maintained in a sterile condition, particularly during storage and prior to placement in the mouth. Otherwise, infection may be transmitted to the bloodstream and become serious. U.S. Pat. No. 6,077,501 describes EDTA used in a denture cleanser composition with other active compositions.
The water supply is also prone to microbial and other types of infections. Water storage devices, as well as water supply and withdrawal conduits, often become infected. The internal surfaces of fluid bearing tubing in medical and dental offices present an environment that is suitable for microbial infection and growth and, in fact, the adherence of microbes and formation of the highly protective biofilm layer is often problematic in fluid storage and supply devices.
There is a need for improved methods and substances to prevent and destroy infections in a variety of environments. Such antiseptic solutions should have a broad range of antimicrobial properties. In particular, the solutions should be capable of penetrating biofilms to eradicate the organisms comprising the biofilms. The methods and solutions should be safe enough to be use as a preventive measure as well as in the treatment of existing infections.